The taking of samples from fluids that are pressurized and/or contain volatile components, i.e. liquids or gases, is performed in a variety of fields including, for example, the chemical, biochemical, pharmaceutical, and in particular the food industry. In the food industry, for example, the chemical and physical parameters of gas-containing beverages such as beer or soft drinks are being determined. Such parameters are particularly difficult to measure in beer, since the latter has a strong tendency to foam even with only a slight and/or momentary loss of pressure. The parameter of interest can for example be the content of dissolved gases such as for example oxygen, ozone, nitrogen, carbon dioxide and carbon monoxide, or in the case of beer the CO2 content and/or the oxygen content of CO2-containing beverages.
Until now, such determinations have been and are being performed mostly on samples that are taken out of a production line and then at least partially depressurized under controlled conditions, so that a state of equilibrium will establish itself between the gas that is still in solution and the gas that has escaped from the fluid. From a measurement of the equilibrium pressure and the temperature one can, in turn, deduce the gas content in the fluid using known physical laws. Besides the gas content, other parameters of the sample can also be determined with suitable additional sensors. Such parameters include for example the turbidity, the color, and the content of further components. The measurement of dissolved gas by means of such expansion methods as well as analytical instruments suitable to perform such methods are disclosed in DE 102 13 076 A1 and DE 44 00 385 A1, among other publications.
A related approach is taken in EP 0 118 964 A1 wherein the sample, after it has been injected into a chamber connected to the production line, is pressed by a piston into a measurement cavity in which an equilibrium pressure can then establish itself between dissolved and free gas as described above.
Another possible solution presents itself in the form of a measurement chamber which is separated from the fluid by a selectively gas permeable membrane. The dissolved gas can diffuse through the membrane into the chamber, where it can be measured by means of conventional sensors.
These methods and instruments provide an indirect measurement of the gas content. The taking of a representative sample from a substantially gas-saturated, pressurized fluid in order to measure a volatile component is not possible without adulterating or changing the sample through outgassing. Furthermore, some of the instruments consist of several chambers and measurement chambers and can therefore not be cleaned without a major effort. However, ease of cleaning is a decisive factor particularly for applications in the food industry.
Instruments for the so-called “near-line” or “at-line” measurement of dissolved gases are distributed by the Mettler-Toledo organization under the trade names “InTap 4000” and “InTap 4004”. They consist of a transmitter, a sensor and a measuring cell which can be connected to the production line through a valve, so that the measurement can be performed in flow-through mode. Arranged downstream of the outlet of the measuring cell is a fixed-aperture flow restrictor which regulates the flow of the fluid through the measuring cell, so that the fluid is not being depressurized already in the measuring cell. The fluid is depressurized after it has passed through the flow restrictor, i.e. after the measurement.
These instruments allow the measurement of certain parameters under the conditions existing in the production line. However, they are likewise complex in their design and have to be laboriously disassembled for cleaning. It has further been found that sediments from the fluid will accumulate on the flow restrictor, obstructing the latter and thereby corrupting the measurements.
Thus, the object of the present application is to develop an improved sampling device which is of compact design, simple to operate and easy to clean, and an analytical instrument comprising the inventive sampling device, as well as a method for taking samples.